The National Institute for Standards and Technology (NIST) is a government facility under the Department of Commerce. "NIST's mission is to develop and promote measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life." At the NIST headquarters site in Gaithersburg, Maryland is the NIST Center for Neutron Research (NCNR). The NCNR neutron source is a 20 megawatt research reactor. The nuclear reactor is neutron beam split core reactor (NBSR), is uranium fueled and moderated with heavy water.

There is are currently twenty-three instruments recieving neutrons at NCNR, one of which is the Filter Analyzer Neutron Spectrometer (FANS), see Figure 1. FANS works in the following manner. When the neutrons leaves the reactor they have a range of energies. These neutron are passed through a copper or polycrystalline graphite monochromator. The monochromator are based on Bragg's Law, the neutrons will scatter from the monochromator at an angle dependent upon their energy. By rotating the sample around the monochromator, these angles/energies can be scanned.

When the monoenergtic neutrons collide with the sample, the neutron's lose energy and scatter in all directions. Having interacted with the sample, these neutrons are once again polychromatic. The neutrons then pass through a series of filters and collimators. The collimators ensure that all neutrons are in line with a detector. The Beryllium and Graphite filters select neutrons of a specific final energy.

The neutrons then hit the detectors and are counted. The detectors are tubes of liquid Helium, see Figure 3. When a Helium-3 atom is hit be a neutron, a photon is given off. That photon is itself detected by a photmultiplier at the top of the tube. FANS currently has forty-eight detectors but in the future, there will be an addition forty-eight installed.

FANS obtains vibrational spectra by measuring the energy transfer from the neutrons to the sample. This can be done beacuse the initial energy of the neutrons are determined by the monochromator and the final energy of the neutron is determined by the filter analyzers.

Our group uses FANS about twice a year. Previous work has resulted in over fifty spectra.